1. Field of the Invention
This invention relates to oxygen depolarized electrochemical cells. More particularly, it relates to metal/oxygen batteries having improved impedance and capacity characteristics.
2. Prior Art
The concept of gas depolarized electrochemical cells is old in the art as evidenced by the numerous issued patents.
It is also known that gas depolarized electrochemical cells can have a "button" cell configuration and be used in a variety of applications such as hearing aids, transistor radios, watches, and miniature electronic calculators.
Zinc/air cells are unique as compared to other button cells in that a void must be provided in the anode portion of the cell. The void is used to accommodate the substantial increase in volume during discharge which occurs, for example, when zinc oxide is produced as the discharge product of zinc anode. The need for this void comes from the sensitivity of the air cathode to pressure. If the air cathode is over compressed there is premature cathode failure and hence cell failure.
However, this void, while providing room for the expansion of the anode material, causes high cell impedence and erratic cell performance when its location in the anode area is uncontrolled.
Sauer et al disclose in U.S. Pat. No. 4,054,726, one method of achieving controlled void space. The method is the use of a compressible expansion body positioned within the anode material. The problem with this method is that excessive space for anode material is lost thereby reducing the cell's capacity.
It would be desirable to have a cell which had a maximum amount of anode material and a void location which was controllable.